1. Field of the Invention
This invention relates to a profile control system which ensures high-precision profile control.
2. Description of the Prior Art
FIG. 1 is a block diagram showing an example of a conventional profile control device. Reference numeral TR indicates tracer head which is provided with a stylus ST for copying a model M, and respective axis displacement components .epsilon..sub.x, .epsilon..sub.y and .epsilon..sub.z in response to the three-dimensional displacement.epsilon. of the stylus ST are each provided after being amplified by an amplifier AMP. A displacement resultant circuit DG receives the above-said axis displacement components .epsilon..sub.x, .epsilon..sub.y and .epsilon..sub.z and operates to provide the displacement .epsilon.=.sqroot..epsilon..sub.x.sup.2 +.epsilon..sub.y.sup.2 +.epsilon..sub.z.sup.2. An adder AD is supplied with the displacement .epsilon. and a preset reference signal .epsilon..sub.0 to yield a difference signal .epsilon.-.epsilon..sub.0, which is provided to each of a command velocity function generator ART and a correcting velocity function generator ARN. The function generators ARN and ART respectively produce correcting and command velocity signals V.sub.N and V.sub.T of such characteristics as shown and apply them to a distributing circuit DC.
In the case of plane profiling, the X- and Y-axis displacement components .epsilon..sub.x and .epsilon..sub.y from the tracer head TR are applied to an index circuit IND, in which the following operations are effected: EQU .epsilon..sub.x /.sqroot..epsilon..sub.x.sup.2 +.epsilon..sub.y.sup.2 =sin.theta. (1) EQU .epsilon..sub.y /.sqroot..epsilon..sub.x.sup.2 +.epsilon..sub.y.sup.2 =cos.theta. (2)
thereby to obtain displacement direction signals sin.theta. and cos.theta., which are provided to the distribution circuit DC.
In the distribution circuit DC, based on the correcting velocity signal V.sub.N, the command velocity signal V.sub.T and the displacement direction signals sin.theta. and cos.theta., X- and Y-axis command velocity signals V.sub.X and V.sub.Y are obtained by the following operations to control the speed of respective servomotors: EQU V.sub.X =V.sub.T sin.theta.+V.sub.N cos.theta. (3) EQU V.sub.Y =V.sub.T cos.theta.+V.sub.N sin.theta. (4)
In FIG. 1, the output signals sin.theta. and cos.theta. from the index circuit IND are configuration signals of the model M detected by the tracer head TR. Where these signals coincide with the configuration of the model M, the profiling is achieved with the command velocity signal V.sub.T given in the tangential direction of the model M but with no correcting velocity signal V.sub.N. That is, the displacement .epsilon. of the stylus ST of the tracer head TR is equal to the reference signal .epsilon..sub.0 and the resultant velocity V is equal to the command velocity signal V.sub.T, i.e. V=V.sub.T.
In actual systems, however, owing to the detection accuracy of the tracer head, an influence of friction between the model M and the stylus ST and the operating accuracy of the index circuit IND, the output signals sin.theta. and cos.theta. from the index circuit IND each have an error with respect to the normal direction N of the model M, as shown in FIG. 4. Since the command velocity is yielded in a direction of 90.degree. relative to an angle .theta. detected with this error, if the stylus ST on the model M at the command velocity V.sub.T, the displacement of the stylus ST decreases by .DELTA..epsilon. and, to correct it, the correcting velocity V.sub.N is generated to direct the resultant velocity to the normal direction of the model M for normal profiling. Accordingly, profiling is always accompanied by the generation of the error and cannot be achieved with accuracy.